In the pending application Ser. No. 725,036, filed Sept. 20, 1976, by Elias E. Solomon, who is also the inventor of the subject matter of the present application there is disclosed a smoke detector which may be of the optical or ionization type. In accordance with that disclosure, the power supply, or the regulator commonly used with the power supply, for the transmitting and receiving circuits is pulsed or strobed for periodic operation. In the case of optical detectors, the light source derives its power from the strobed power supply or regulator directly or indirectly and it, of course, is also periodically energized. A considerable reduction in power consumption compared to continuously operating systems is achieved. Still further savings in power consumption and uniformly low current demand are obtained by utilizing a reservoir which is never fully discharged between pulses.